Mali was in a state of crisis on Thursday as mutineering soldiers seized power and announced a military curfew.

A spokesman for the mutineers – who have formed themselves into a National Committee for the Restoration of Democracy and State (CNRDR) – have said the constitution is suspended and democratic institutions dissolved.

In video footage now circulating on YouTube, Captian Amadou Haya Sanogo, who is emerging as the leader of the CNRDR, appeared on Malian TV to announce an immediate curfew and appeal for calm after hours of gunfire overnight in the capital, Bamako.

Since the 1990s Mali has been known for being one of the most stable democracies in west Africa. Sanogo was a previously little known middle-rank solider in Mali's army.

A spokesman for the CNRDR said it would oversee a transition back to democratically elected power.

"The CNRDR … has decided to assume its responsibilities by putting an end to the incompetent regime of Amadou Toumani Toure," said Amadou Konare.

"We promise to hand power back to a democratically elected president as soon as the country is reunified and its integrity is no longer threatened," he said.

However, the whereabouts of Toure remained unclear.

"The president is not in the palace, the soldiers have taken him to another location," said Cheick Oumar Sissoko, leader of Mali opposition party African Solidarity for Democracy and Independence. "We think he has been taken to another military base."

Toure, a former military commander, overthrew a military regime in a coup in 1991, overseeing a transition to democracy, and was first elected in 2002.

Anger towards his regime has been mounting in the army since January when a rebellion led by rebels from the Tuareg ethnic group began attacking towns in northern Mali. The rebellion, which has displaced 200,000 civilians in areas already affected by food shortages, has been strengthened by arms and soldiers returning from Libya, where many Tuaregs supported Muammar Gaddafi.

"Mali's army has been very angry since the Tuareg rebels started attacking towns in the north, said Sissoko. "They say they are very disappointed that the government has not done more to help them with equipment or food, and that the government has no capacity to resolve any of those problems. So they decide to stop them and now to try to continue the democracy with new elections."

In a statement, the UN secretary-general, Ban Ki-moon, called for calm and stated that grievances had to be settled democratically.

Jean Ping, the head of the commission of the African Union continental grouping, said he was "deeply concerned by the reprehensible acts currently being perpetrated by some elements of the Malian army".